Allow renames to be prepared for here-documents

[rcjsuen]

FROM alpine
RUN <<EOT
EOT

const lib = require("dockerfile-language-service");
const service = lib.DockerfileLanguageServiceFactory.createLanguageService();
const document = `FROM alpine
RUN <<EOT
EOT`

console.log(service.prepareRename(document, { line: 1, character: 8 }));

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